The present invention relates to a method and circuit for correcting a record timing in recording of digital data on a record medium in a magnetic recording apparatus, such as a magnetic disc storage device, and more particularly to a method and circuit for correcting the record timing to obtain a correct playback timing of data reproduced from a record medium.
In general, a magnetic disc storage device in a computer system stores information on a magnetic disc in the form of digital data consisting of "0"'s and "1"'s. In recent years, in order to store more information on the magnetic disc, it has been required to decrease the minimum distance between adjacent magnetization transitions. However, in order to assure proper bit detection, it is necessary to make the interval between bits more than a certain value.
In order to meet the above requirements, there have been proposed a 3PM (3-position modulation) system in which original data consisting of three bits is converted on a record data consisting of six bits and a conversion system in which a limitation is imparted to the above conversion to shorten the processing time (U.S. Pat. No. 3,689,899; Japanese Laid-Open patent application 7641/73).
However, the prior art methods have a problem in that they cannot exactly reproduce data when the interval between record bits stored on the magnetic disc is reduced to attain a high recording density and when the signal reproduced from the record medium through a predetermined discrimination window, called a data separation window, is converted to a pulse.